There is conventionally known an accelerator for controlling the driving state of a vehicle in response to depressing an accelerator pedal. In the accelerator, generally, an accelerator pedal whose turning shaft is supported by a bearing part is turned in a forward direction by a depressing force whereas the accelerator pedal is turned in a reverse direction by the urging force of a spring to make the accelerator pedal abut against a stopper to limit its reverse turn.
Among the accelerators like this is an accelerator of the acceleration-by-wire type in which an accelerator is not mechanically coupled to the throttle device of a vehicle as disclosed in, for example, European Patent Application Publication No. 0748713A2. In the accelerator of the acceleration-by-wire type, the turning angle of an accelerator pedal is detected by a turning angle sensor as disclosed in, for example, Japanese patent document JP-2003-185471A, and a signal indicating the detection result of the sensor is outputted to the control unit of the throttle.
FIG. 28 schematically shows a state where an accelerator pedal abuts against a stopper, that is, an accelerator pedal is totally closed in an accelerator of the conventional acceleration-by-wire type. When the accelerator pedal is totally closed, as shown in FIG. 28A, the force receiving part 102 of an accelerator pedal 101 continuously receives the urging force Fs of a spring 103. For this reason, when the accelerator is left in high temperature surroundings, the force receiving part 102 and a turning shaft 104 of the accelerator pedal 101, and a stopper 105 and a bearing part 106 to which loads are applied by these elements 102 and 104 undergo plastic deformation such as creep. In particular, this plastic deformation becomes large when these elements 102, 104, 105 and 106 are made of resin. When this plastic deformation occurs, as shown in FIG. 28B, the force receiving part 102 of the accelerator pedal 101 is shifted in position in a direction in which the urging force Fs is applied, whereas the turning shaft 104 of the accelerator pedal 101 is shifted in position in a direction opposite to the direction in which the urging force Fs is applied. In this manner, the force receiving part 102 and the turning shaft 104 are shifted in position in opposite directions, whereby the accelerator pedal is turned although the accelerator pedal is not depressed. Hence, as a result, the output signal of the turning angle sensor indicates an erroneous turning angle.
FIGS. 29A and 29B show a state where the accelerator pedal is totally closed in the turning angle sensor disclosed in Japanese patent document JP-2003-185471A. Here, in FIGS. 29A and 29B, a three-dimensional rectangular coordinate is defined in which a Z direction is aligned with the axial direction of a turning shaft of an accelerator pedal (direction vertical to the surface of paper). When the accelerator pedal is totally closed, as shown in FIG. 29A, there is a case where core parts 112, 113, which are arranged side by side in an X direction, of a core 110 are shifted in position from each other in a Y direction because of assembly tolerances. When the core parts 112, 113 are shifted in position from each other, the core part 112 is closest to one of the plane portions 122, 123 of yokes 120, 121 which face each other in parallel in the Y direction across the core 110 and the core part 123 is closest to the other of the plane portions 122, 123. As a result, magnetic flux passes through a magnetic gap formed between the core parts 112, 113 which are closest to the plane portions 122, 123, respectively, to bring magnetic resistance into unbalance, whereby magnetic flux flows through a Hall device 111 sandwiched between the core parts 112, 113. Further, when the turning shaft is shifted in position in the Y direction in this state by the above-described plastic deformation and the like as shown in FIG. 29B, the yokes 120, 121 fixed to the turning shaft are relatively shifted in position in the Y direction with respect to the core 110 fixed to the bearing part. As a result, the magnetic gaps between the plane parts 122, 123 and the core part 112, 113 closest to them are changed in width, respectively, to bring magnetic resistance in the core 110 into large imbalance, which results in passing more magnetic flux through the Hall device 111. Hence, although the accelerator pedal is not turned, the output signal of the Hall device 111, that is, the output signal of the turning angle sensor varies and hence the output signal indicates an erroneous turning angle.